$ { \left[\begin{array}{rr}{2} & {-1} \\ {-1} & {-1}\end{array}\right]+\left[\begin{array}{rr}{4} & {1} \\ {-1} & {0}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{2}+{4} & {-1}+{1} \\ {-1}+{-1} & {-1}+{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{6} & {0} \\ {-2} & {-1}\end{array}\right]}$